Patent GB-676070-A (GB)
Title: Improvements in or relating to knife sharpening mechanisms
Inventor: CLARK FREDERICK GEORGE
IPC: B24B3/36
Filed: 1950-11-08
Abstract: 676,070. Sharpening machine cutters in situ. EASTMAN MACHINE CO. Nov. 8, 1950, No. 27283/50. Class 60. [Also in Groups VIII and XXIV] In knife sharpening mechanism for a cutting machine in which grinding means are traversed to and fro along the knife edge, the traversing mechanism comprises a rotatable screw shaft having right and left hand threads and movable axially for causing travel of the carriage for the grinding means, two nuts held against axial movement and engaging respectively the right and left hand threads of the shaft, latch means for alternately holding one nut from rotation and permitting the other nut to rotate, and means actuated by the longitudinal movement of the screw shaft for operating the latch means to cause reversal of the direction of travel. A cutting machine comprises a base 20 adapted to rest and be moved about on the supporting table for the lay of material to be cut, an upright standard 21 secured on the base and supporting the stationary frame 22 of an electric motor which reciprocates a knife 23 in a vertical guide at the front of the standard through drive mechanism including a crank wheel 24 on the front end of the horizontal shaft of the motor; a presser foot 26 is provided at the lower end of a guard bar 27 extending vertically in front of the knife and vertically adjustable on the machine to set the presser foot at different levels according to the thicknesses of different lays or piles of material. The knife is sharpened by two narrow abrasive belts 30, 31 disposed at opposite sides of the knife to travel crosswise of the knife in sharpening contact with opposite sides of the knife edge, around front drive pulleys 32, 33 and rear spring-actuated belt-tensioning pulleys 34, 35 the belts being power driven by the knife-operating motor. The pulleys 32-35 are carried on the underside of a carriage 36 arranged to travel up and down lengthwise of the knife edge. The belt drive pulleys 32, 33 are fixed on the lower ends of non-circular e.g. square, vertical shafts -40, 41 rotatable in but axially movable with carriage 36; the shafts extend up into a housing or cover piece 38 and are axially movable through but rotate with intermeshing pinions 42,43 held from axial movement in the housing 38 and oppositely rotated by a pinion 44 on a shaft 45 driven through spiral gear train 46-48 by a wheel 49 movable into and out of contact with crank wheel 24. The wheel 49 has a friction tyre and is carried by a pivotally mounted bell crank lever 51 loaded by a spring 53 so as to. urge the wheel 49 into engagement with the crank wheel 24. A push rod 57 is slidable vertically in housing 38 with its lower end projecting to be engaged by grinder carriage 36, so that when the latter is in its upper position it raises .push rod 57 and shifts lever 51 against the action of spring 53 to move driven wheel 49 out of contact with crank wheel 24. The grinder carriage 36 is reciprocated by a screw shaft 60 having crossing right and left hand screw threads; the shaft is journalled in the grinder carriage 36 but is held against axial movement relatively thereto by thrust collars. The non-circular lower end of the shaft carries a gear 62 driven through gears by the shaft 41. The screw shaft 60 extends vertically up through the housing 38 and passes through two nuts 67, 68 one nut having a left hand thread engaging the left hand thread of the shaft and the other nut having a right hand thread engaging the right hand thread of the shaft; the nuts are restrained against axial movement relative to the housing 38. The nuts are respectively restrained against rotation by a pivoted latch 70 having a detent 72 adapted to engage wings 73 on the nut 67 and a detent 74 adapted to engage wings 75 on the nut 68. The latch 70 is urged by a spring 77 to the position in which the dog 74 holds the nut 68 against rotation, but can be swung about its pivot, against the action of the spring 77 by a link 79 provided with a handle 81. A pivoted latch holding member 84 acted on by spring 89 has an arm 86 adapted to engage a shoulder 87 on the latch 70. To start the sharpening mechanism, the handle 81 is depressed thus swinging the latch 70 from the position in which it locks the nut 68 into the position in which it locks the nut 67; during this movement of the latch 70 there is a neutral position in which both nuts are free to rotate, this permitting downward movement of the carriage 36 by the spring 53 acting through the push rod 57, accompanied by actuation of the bell crank lever 51 to force the driven wheel 49 into contact with the crank wheel 24 to cause rotation of the screw shaft 60. Further movement of the latch 70 from its neutral position into the position where it locks the nut 67 causes downward travel of the screw shaft and grinder carriage 36; the latch 70 is held in this position by the member 84. The upper end of the screw shaft 60 is provided with a reversing sleeve 93; to permit adjustment, the sleeve is threaded on to a threaded portion 95 of the shaft and secured by a lock nut 96. As the screw shaft moves into the lower portion of its stroke the reversing sleeve 93 engages the arm 90 of the member 84 which is thus swung, against the action of the spring 89, so that the arm 86 is disengaged from shoulder 87 of latch 70; the spring 72 then moves the latch to the position in which the lower nut 67 is freed and the upper nut 68 locked, whereupon the screw shaft and carriage 36 move upwardly. The upward movement is stopped when a portion of the carriage engages the push rod 57 which swings the bell crank lever 51 about its pivot against the action of the spring 53 and thus moves the driven wheel 49 out of contacts with the crank wheel 24, so stopping the operation of the sharpening mechanism and holding the carriage 36 in its upper position, where it remains until the handle 81 is again actuated by the operator. To avoid the possibility of damage to the machine if the operator holds the handle 81 depressed when the mechanism is about to begin to raise the grinder carriage, the link 79 carries a pin 98 located in the path of movement of the holding member 84 as it swings out of position to engage the shoulder 87 of latch 70; thus the positive swinging of the holding member 84 by means of the reversing sleeve 93 forces the link 79 upwardly so that the latch 70 disengages the wings of the lower nut 67. The holder member 84 has a projection 99 for actuation by the operator. To avoid damage to the machine in case the sharpening mechanism is actuated before the presser foot has been moved to its lowest position, the presser foot bar 27 is locked against upward movement by the goods which are being cut, but is free to move. downwardly if engaged by the downwardly moving grinder carriage. A cam member 105, the outer end of which is notched to engage the presser foot rod 27 which is of square cross-section, is pivoted on the machine frame and biased by a spring 110 to move into a position in which the arm extends downwardly at a slight inclination from its pivot to the rod 27, thus preventing upward movement of the rod while permitting downward movement. The cam member 105 is moved out of engagement with the presser foot rod by a crank handle 117 operating through bevel gears 114, 115; a spring may be provided to return the handle to normal position in which the presser foot rod is locked against upward movement.